What caused my melted piston?

[Ratickle]

The engine will not run more than a few seconds with pre-ignition. The only way to control pre-ignition is just keep any pre-ignition sources at bay. Spark plugs should be carefully matched to the recommended heat range. Racers use cold spark plugs and relatively rich mixtures. Spark plug heat range is also affected by coolant temperatures. A marginal heat range plug can induce pre-ignition because of an overheated head (high coolant temperature or inadequate flow). Also, a loose plug can't reject sufficient heat through its seat. A marginal heat range plug running lean (suddenly?) can cause pre-ignition.


http://www.enginelogics.com/detonation.html

Great read Ted. Thanks. It would be nice to take that article and add pictures of all the items he described. Then have it here for the future.

[Tomas Wallin]

I´d Tomas go with the loose plug theory going too hot but also I´m interested about your head and intake gaskets sealing properly ?

And let´s just not forget a piston ring land failure.

I mean it detonated and only oil and too lean a combustion in a single cylinder would do this.

The leak down was - cold, very cold... 2-6% on all 8 cylinders, so it was nice and tight. Total seal gapless rings, MLS head gaskets.

The intake gaskets looked just fine! No signs of any leaks.

[Tomas Wallin]

Is it carb or injection?

How long did it take for that to happen total do you think? Sure made a mess......

2x Holley 800cfm

After a few warmup passes I made one wot pass for maybe 2miles, turned back and made one more and after about half the distance it lost some power and I pulled off.

[MikeyFIN]

The leak down was - cold, very cold... 2-6% on all 8 cylinders, so it was nice and tight. Total seal gapless rings, MLS head gaskets.

If the leakdown was at Cold 2-6 how do you think the Rings had any movement left while heated..

I mean on Audi WTCC racecars we had up to 20% leakdowns cold also the same with Turbocharged experimentals and Audi Sports head boss from Ingolstadt at the time told not to worry about that as they will seal up while getting warm especially charged engines and they did up to your numbers.

I never do a leakdown cold... just doesn´t make sense IMO.
As a machinist by profession I think I know something.

Tomas you still work for Scania..I think you could get some inhouse help?

But How was the Head gaskets?

[Tomas Wallin]

If the leakdown was at Cold 2-6 how do you think the Rings had any movement left while heated..

I mean on Audi WTCC racecars we had up to 20% leakdowns cold also the same with Turbocharged experimentals and Audi Sports head boss from Ingolstadt at the time told not to worry about that as they will seal up while getting warm especially charged engines and they did up to your numbers.

I never do a leakdown cold... just doesn´t make sense IMO.
As a machinist by profession I think I know something.

Tomas you still work for Scania..I think you could get some inhouse help?

But How was the Head gaskets?

The low leak down is because of the gapless rings, the ring gaps are where they're supposed to be on the plus side. I ran one season with them and everything worked great, the leakdown was the same when new.

No, I quit there a year ago, couldn't find much inhouse help there anyway.

The head gasket looked like this:

[MikeyFIN]

The low leak down is because of the gapless rings, the ring gaps are where they're supposed to be on the plus side. I ran one season with them and everything worked great, the leakdown was the same when new.

No, I quit there a year ago, couldn't find much inhouse help there anyway.

On blown engines I don´t like gapless rings (because of the heat variations running I like to have things a little on the loose side so I don´t need to worry ) or MLS gaskets but that´s just me.

OK so you had no problems before, hmmmm ???

Howabout a water cooling problem on the head, the right side runs warmer and the middle ones seems to have gotten some coolant problems ?

Strange is what it is... but the more I think the more it seems like oil in the combustion or cooling problem which could lead to detonation problems. The cylinders are perfect so the water is at least up to there.

The 1-2 o´clock position looks a bit doubtful but detonation will do that quick, hard to see without a mag.glass..

[Tomas Wallin]

On blown engines I don´t like gapless rings (because of the heat variations running I like to have things a little on the loose side so I don´t need to worry ) or MLS gaskets but that´s just me.

OK so you had no problems before, hmmmm ???

Howabout a water cooling problem on the head, the right side runs warmer and the middle ones seems to have gotten some coolant problems ?

Strange is what it is... but the more I think the more it seems like oil in the combustion or cooling problem which could lead to detonation problems. The cylinders are perfect so the water is at least up to there.

The 1-2 o´clock position looks a bit doubtful but detonation will do that quick, hard to see without a mag.glass..

There's no rust what so ever in the heads nor the block.

Why do you think it seems like oil in the combustion? It definately started where the spark plug points if you look at this pic.

[MikeyFIN]

Was there a ring land failure at the top piston ring?

If yes thats where the 7-8 o´clock meltdown started because of slight oil in the combustion.
Doesn´t need much to lower the octane of the combustion mix to a mess and when you have the spark there also voilá we have a dish served...

My theory is that the head for a while run dry and heated which lead to oil ( rings butting because of too much heat ) in the combustion and from thereone the spark functioned as a small torch for a millisecond.

What do you think ?

[Tomas Wallin]

Was there a ring land failure at the top piston ring?

If yes thats where the 7-8 o´clock meltdown started because of slight oil in the combustion.
Doesn´t need much to lower the octane of the combustion mix to a mess and when you have the spark there also voilá we have a dish served...

My theory is that the head for a while run dry and heated which lead to oil ( rings butting because of too much heat ) in the combustion and from thereone the spark functioned as a small torch for a millisecond.

What do you think ?

The head ran dry of water or fuel?

How would I know if the ring land failed? The piston got pretty warm since it began to sink just between the piston center and 7-8 o'clock. But what happened first? If it sinks I bet the ring land will break pretty soon as well?

Then the oil started getting in and it detonated to hell

[MikeyFIN]

Of water... as you have a Carb engine.
Offtopic
My team boss ignored the same thing on our formula ford rollout in the british series last year and lost 5 engines because of that.
I wanted to check the water was flowing immidately while the kid was coming back to the pit gate just to look into problems and leaks but Dad thought otherwise...

Kid told me next year dad ain´t coming along at all... or he doesn´t race.

In Karting I never did forget the water checks (couldn´t afford it)... on a boat with Raw water cooling I like to see a good flow too and Daredevil too...thats one of the reasons why he runs dry...
Right Scotty !!!?

Back on track.
Check the inside of the piston..do you see fractures along the top compression ring groove.
When things heat up it doesn´t necessarily break because it goes soft but you´ll see fractures or something.
If the ring land is intact the compression rings just got too much heat and butted and gave a mix of air and oil to let the spark plug be a torch.

That´s my (long) shot theory.

[Chris]

A loose plug would lose a portion of it's heat sinking capability, but I would think the ground would melt away quickly and the plug would stop firing.

[MikeyFIN]

Chris I agree with you, a Loose plug would just die.

[Ted]

A loose plug would lose a portion of it's heat sinking capability, but I would think the ground would melt away quickly and the plug would stop firing.

Note that in the article I posted it says "The engine will not run more than a few seconds with pre-ignition. " I think the plug got so hot that it became like a top fueler at the end of the track, the plugs are completely consumed and the engine is dieseling. Also with a good ignition system you would simply start scattering spark to the thread or head area, MSD or Crane can jump a spark over a 1/2" gap.

[MikeyFIN]

But the MSD would not detonate and if it would diesel it would´ve not shut down immidiately... it would´ve kept dieseling until a hole in the piston

[Tomas Wallin]

But the MSD would not detonate and if it would diesel it would´ve not shut down immidiately... it would´ve kept dieseling until a hole in the piston

The compression was really bad when I turned it off since it smoked alot through the breathers and also through the oil pan gasket, with that bad comp I guess the dieseling would have stopped and only took place at high revs?

Would it be able to diesel on only one cylinder?

[Ted]

But the MSD would not detonate and if it would diesel it would´ve not shut down immidiately... it would´ve kept dieseling until a hole in the piston

He pulled out of it.

The compression was really bad when I turned it off since it smoked alot through the breathers and also through the oil pan gasket, with that bad comp I guess the dieseling would have stopped and only took place at high revs?

Would it be able to diesel on only one cylinder?

Yes, absolutely, all you need is a heat source hot enough to ignite the A/F mixture. Most blower motors are on the edge of dieseling anyway so even a small change is enough to start a hot spot. As the piston burned away and it started to lose compression and use oil it probably ended the event.

[Tomas Wallin]

He pulled out of it.




Yes, absolutely, all you need is a heat source hot enough to ignite the A/F mixture. Most blower motors are on the edge of dieseling anyway so even a small change is enough to start a hot spot. As the piston burned away and it started to lose compression and use oil it probably ended the event.

I meant, would it be able to run on only one cylinder that's dieseling if the others are turned off.

[Tomas Wallin]

A loose plug would lose a portion of it's heat sinking capability, but I would think the ground would melt away quickly and the plug would stop firing.

That was one of the opinions I got when I showed the piston to some folks, that the spark plug died. But when it dies it's warm enough to diesel (as Ted said) if it dies of heat of course. But I couldn't find any reason to why it should have died - until now...

[Ted]

I meant, would it be able to run on only one cylinder that's dieseling if the others are turned off.

No, by that point it probably couldn't develop enough power to even turn the blower. You probably failed this thing in the last pull within second of when you lost power, blower motors leave no margin, especially under the load of a boat.

[MikeyFIN]

I meant, would it be able to run on only one cylinder that's dieseling if the others are turned off.

Nope but like you said..it smoked already and you lost compression so where did it go if not a hole somewhere... because of detonation ..aka dieseling.